We do begin with the murder case in Florida that began with a fight over loud music. Michael Dunn is claiming self-defense. He may seek protection under Florida's stand your ground law. ABC's Steve osunsami has the story. Reporter: This morning his attorneys seat a jury for his murder trial, 47-year-old software developer Michael Dunn is pleading not guilty saying what happened outside this Florida gas station is a clear case of self-defense. 911, may I please have the ambulance? Reporter: They say it started over loud music coming interest this red SUV. Dunn and his girlfriend had left his son's wedding in November 2012 and was in the car outside asking four black teenagers in the durango to turn it down. Hey, would you mind turing that down? And they -- Reporter: In this interrogation video he explained that they then turned it back up. When he complained they started yelling from inside the vehicle. That's when Dunn says he saw something point at him from the SUV. Either a barrel or a stick but, sir, there -- they're like we're going to kill you. Reporter: Dunn says he grabbed a 9 millimeter fired four shots and walked outside his car as the SUV backed away. Jordan Davis, just 17 and in the backseat was killed. His three teenage friends survived. To justify what I did, on that second volley other than saying I thought they were going to be shooting back. Reporter: Police found no weapons in the SUV. Davis' mother heartbroken. Like vigilanteism. It's not just about Jordan. A lot of other people have died behind these laws. Reporter: The lead prosecutor is the same state attorney who failed to convict George Zimmerman who argued self-concerns in the shooting death of another black 17-year-old, trayvon martin. Steve osunsami. Let's talk about it with Dan Abrams. We just saw the picture of trayvon martin there. A young black man is dead right now. Stand your ground is being talked about. Are the cases really similar? Look, apart from the fact that they were both unarmed, they're not that similar and the key difference is that in the George Zimmerman case in my view the most important piece of evidence was the fact that he had injuries on the back of his head. Why was that so important? Because that forced the prosecutors to prove beyond a reasonable doubt that he didn't actually fear great bodily injury. Didn't reasonably believe he could have that or death inflicted upon him. Here there is no evidence of injury. There is no gun. It's that combination that is going to make this a much, much harder defense than George Zimmerman. Does he mean he cannot succeed? No, and, look, the key is really going to be self-defense. He did not seek a stand your ground hearing. Remember, one of the most controversial parts of it is it lets you try and avoid a trial and go to a judge and say I shouldn't be tried at all. There wasn't a stand your ground hearing here so it's stand your ground/self-defense, the most important question will be was he reasonable in his belief that he was trying to prevent death or great bodily injury. He says -- The authorities would say there's inconsistent statements in what he said so this -- I think that this is a much harder defense than was the case of George Zimmerman. Dan Abrams, thanks very much. Such a tragic loss of life.

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